1. Field of the Invention
This invention relates to a method of recovering lead-free solder used in printed circuit boards employed in electronic equipment such as televisions, videos, and computers.
2. Description of the Related Art
A printed circuit board for use in electronic equipment typically comprises a polymeric substrate having a circuit formed on a surface thereof with copper foil, silver paste, or other materials. Electronic components are usually mounted on mounting portions of the circuit with solder.
Traditionally, solders for use in printed circuit boards have been lead-based solders containing a large proportion of lead. However, in recent years, due to increased awareness of the potentially harmful effects on the environment of lead-based solders, lead-free solders which do not contain lead have come to be widely used for all types of electronic equipment.
The most common lead-free solders are tin-based solders, in which Sn is combined with one or more additional alloying elements such as Ag, In, Sb, or Bi. The alloying elements employed in lead-free solders tend to be expensive. Since electronic equipment containing printed circuit boards employing lead-free solders is discarded in enormous quantities, the solder in the printed circuit boards represents a huge potential source of valuable metals. However, an economically practical method of recovering lead-free solders from discarded printed circuit boards has yet to be developed, so at present, printed circuit boards in discarded electronic equipment are usually disposed of without the lead-free solder thereon being recovered, so the economic potential of the lead-free solder is not being realized.
The present invention provides a method of efficiently and economically recovering lead-free solder from printed circuit boards.
In one form of the present invention, discarded printed circuit boards are sorted according to the alloying elements contained in the lead-free solder used therein. The solder is recovered from the sorted printed circuit boards by heating the printed circuit boards to melt the solder and separate the molten solder from the printed circuit board. The molten solder is then collected. Because the printed circuit boards have been sorted prior to melting the solder, different types of solder can be prevented from mixing with each other, so the solder can be economically refined to permit its reuse.
After recovery of the solder, the printed circuit board may be discarded, recycled, or otherwise processed.
Preferably each printed circuit board to be sorted is provided with an indicator indicating the alloying elements in the solder used in the manufacture of the printed circuit board, and the printed circuit boards are sorted based on the information in the indicators.